The present invention relates to ice making machines and particularly to control methods for automatic ice making machines. The invention particularly relates to a control system that includes one or more of the following: automatic restart, condenser fan control, harvest and freeze cycle duration control, and timing for changing a water filter.
Numerous automatic ice making machines have been developed over the years. Most of these machines have been free-standing units that are connected to electrical and water supplies and make ice using a standard refrigeration system. The ice machines often have a control system which automatically operates the machine through freeze and harvest cycles, and which turns the machine off when sufficient supplies of ice have been made.
Many times an ice machine is located in a place where the noise of the ice machine is objectionable. For example, an automatic ice making machine may be located under the counter in a kitchen, in a conference room, or in a sky box at a sports stadium. While the noise from the ice machine does not present a problem during most hours of the day, there may be times when individuals in its vicinity would like to shut the ice machine off, such as when speaking on the telephone in the kitchen, or when entertaining guests. As frequently happens, people will unplug or turn off an ice machine in these circumstances, and then forget to plug it back in or turn it back on when their conversation is over or the guests leave. Often the fact that the ice machine has been turned off is not noticed until it is too late to restart the machine and produce adequate quantities of ice before the ice is needed.
Such ice machines come in all sizes, from large machines that make hundred of pounds of ice in an hour, to smaller machines which make a few pounds of ice an hour. The control systems for such machines vary from sophisticated to simple.
Many cube ice making machines use a hot gas bypass valve to harvest the cube ice by sending hot refrigerant from a compressor directly to an evaporator mounted on the back of a cube forming evaporator plate. Instead of freezing water into ice, the evaporator then melts the ice. Knowing when to start and end the harvest cycle is important. The maximum efficiency of the machine requires that the harvest cycle be started when ice has formed sufficiently, and stopping the harvest cycle as soon as the ice is released from the ice forming evaporator plate. Prior art patents disclose the use of ice thickness sensors to initiate a harvest cycle, and an electro-mechanical sensor, such as a water curtain switch, to detect when the ice cubes fall off of the ice-forming evaporator plate. There are numerous other control sensors and mechanisms to start and stop the harvest cycle.
One problem with many of the sophisticated control systems is that they require components that add significant cost to the ice making machine. On relatively small ice machines, where the manufacturing cost is minimized, a trade off is made in that the control system does not operate the machine in the most efficient manner. For example, in some ice machines, the durations of the freeze and harvest cycles are based on a sensor which measures the temperature or pressure of the refrigerant on the suction side of the compressor. Other systems use a thermostat on the evaporator or outlet of the evaporator. In these systems, when a predetermined temperature is reached, the machine changes to a harvest cycle, and when another temperature is reached, they change back to a freeze cycle. When the ambient air is warmer, the freeze cycle duration is longer. Some such systems include an adjustment knob so that the cycle time can be increased or decreased as desired if ice cube thickness is too great or too small.
One problem with such a simple control system is that it does not automatically take into account several variables. For example, the optimum freeze and harvest cycle durations will depend not only on ambient air temperatures, but on such factors as how clean the condenser is, and whether any foreign objects are blocking the flow of air past the condenser. The adjustment knob can be used to adjust the cycle times as these factors change, but this often requires a service technician, or is not done properly. As a result, the machines may not produce sufficient ice, and they have higher operating costs than necessary.
U.S. Pat. No. 5,878,583 disclose an ice machine that solves many of the aforementioned problems, using a simple control mechanism to initiate a harvest cycle without the use of a water level sensor or ice thickness sensor, which is inexpensive so that it can be used on small ice machines but which greatly improves the efficiency of the machine compared to simple control systems known theretofore. The improved control system starts and stops the harvest cycle dependent on varying conditions, including not only ambient temperature, but increasing amounts of dirt on condenser coils and partial blockage of air flow past the condenser coil.
However, even further improvements are desirable. First, ice machines operate in different ambient conditions, which sometimes change over the course of a year or even throughout the day. The efficiency of the operation of the ice machine can be improved if the fan used to cool an air-cooled condenser is only used when needed. For example, during the freeze cycle, the fan should be operating to remove as much heat from the refrigerant as possible. However, if the ice machine uses a hot gas defrost in the harvest cycle, the defrost time may be unnecessarily long, or not even occur at all, if the condenser fan operates continuously. On the other hand, if the fan is off during every defrost cycle, more heat may build up in the refrigeration system than is needed, depending on the ambient air temperature. For example, in hot ambient conditions, the condenser fan should normally be operating during harvest, or the harvest bypass refrigerant will get too hot and take longer than necessary to cool back down when the machine switches back over into a freeze mode. Hence, it would be beneficial to be able to control the condenser fan to only operate during harvest cycles in which it is needed.
U.S. Pat. No. 4,257,237 discloses a spray-type ice machine in which a first thermistor is used to sense the ambient air temperature and control the harvest duration. Another thermistor is used to control the condenser fan during the harvest cycle. The second thermistor senses high temperatures in the condenser and the fan is turned off and on based on the condenser temperature to keep the condenser in a desired temperature range. One drawback to this system is that if the temperature gets to a point that the fan is turned on, it is very possible that more heat than was needed for efficient defrost has already built up in the system, and the next freeze cycle will be unnecessarily long because the extra heat has to be removed.
Ice machines that use a capillary tube instead of a TXV valve to control the flow of refrigerant to the evaporator are particularly in need of control improvements. While a capillary tube is less expensive that a TXV valve, capillary tubes are generally only used on machines that are used where there is not a wide swing in the ambient temperature. If someone wanted to put an ice making machine in an unheated garage, it might be called on to operate over ambient temperatures ranging from 20° F. to 120° F. It would be beneficial if a control system could be developed that would allow ice machines with capillary tubes to be efficiently operated, even if the machine were located in an area with a wide swing of ambient temperatures.
There are instances where the freeze cycle duration and/or harvest cycle duration for a given ice machine would be beneficially altered for a given machine, such as where a user wishes to have larger or smaller ice cubes, or to deal with variations in the refrigeration components from one machine to the next. However, if the freeze and/or harvest cycle times were totally under the control of the end user, many people would not know how to properly adjust the times. Thus it would be beneficial if a control system for a ice making machine could be developed that had a simple way to adjust the freeze and/or harvest cycle duration, while using a control system that automatically accounted for most variables (such as ambient air and inlet water temperature, and any dirt build up on the condenser) to efficiently produce ice.
Another drawback relating to many automatic ice making machines is that several different models of ice machine are made by a manufacturer, and the control board used in each model of machine has to be separately designed, produced and kept in inventory until that model of ice machine is being manufactured. For example, some models of ice making machines are very similar to one another in size and components, but differ in the size of ice cube that they make. Unfortunately, the shape of the ice forming mold has a significant impact on the optimum duration of the freeze and harvest cycles. Thus, just using a different evaporator/ice-forming mold to make different sizes of cubes in the otherwise identical machine would require a manufacturer to stock two different control boards. The cost for the separate design, production and inventory of multiple control boards must, of course, be recouped in the sales price of the machine. Thus there would be a great benefit if a control system could be developed that could be used to control several different models of ice machines but used on a common control board.
Water filters are sometimes highly desirable on automatic ice making machines, where the water supply includes objectionable minerals, odors or other contaminants that could end up in the ice. Most water filters are designed to be used for a period of time and then replaced. If the water filter is not replaced soon enough, it will loose its efficacy. On the other hand, if it replaced more frequently than needed, unused filtration capacity is paid for and wasted. Many appliances that include a water filter have an indicator to show that the filter should be changed, but these indicators are typically based strictly on the length of time that the appliance has been running. One problem with replacing the water filter on an automatic ice making machine is that the amount of water used by the machine, and hence cleaned by the filter, may vary greatly, depending on the location and type of use to which the machine is put. Therefore there would be great benefit in a control system that would remind a user to change a water filter at an appropriate time for the specific machine on which it is installed.